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Fullerene (C 60 ) has been demonstrated, using vapor deposition, to be a good electron transport layer (ETL) and different thicknesses have been utilized in n-i-p configuration perovskite solar cells. However, an underlying reason for the variation in thicknesses, which hinders the reproducibility of perovskite solar cells employing a C 60 ETL, has not been well-examined. This study reveals that the surface roughness of the conducting glass, such as fluorine doped tin oxide (FTO), affects the photovoltaic performance while optimizing the thickness of the vacuum deposited compact C 60 ETL. A low-thickness C 60 ETL retains a surface roughness and Ohmic behavior similar to bare FTO due to physical defects at the C 60 /FTO interface. Increasing the thickness further reduces the defects at the C 60 /FTO interface and facilitates an enhanced electron extraction from a vacuum co-deposited methyl-ammonium lead iodide perovskite light absorber. As a result, a perovskite solar cell with a homogenously covered C 60 ETL on an FTO substrate delivers a power conversion efficiency of 14.63%. These comprehensive characterizations support the finding that suppression of defects at the C 60 / FTO interface results in an improved photovoltaic performance. This work demonstrates that the surface roughness of FTO needs to be considered for a decisive compact ETL for enhanced photovoltaic performance and reproducibility.

Hole transporting layers (HTLs) play a crucial role in the realization of efficient and stable perovskite solar cells (PSCs). Copper phthalocyanine (CuPc) is a promising HTL owing to its thermal stability and favorable band alignment with the perovskite absorber. However, the power conversion efficiency (PCE) of PSCs with a CuPc HTL is still lagging behind highly efficient solar cells. Herein, a p-type tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) is employed as an interlayer between the perovskite and CuPc HTL in all-vacuum deposited PSCs. The F4-TCNQ interlayer improves the conductivity of both MAPbI3 and CuPc, reduces the shunt pathway and facilitates an efficient photoexcited holes transfer from the valance band of the MAPbI3 to the LUMO of the F4-TCNQ. Consequently, the best solar cell device with an F4-TCNQ interlayer achieved a PCE of 13.03% with a remarkable improvement in fill factor. Moreover, the device showed superior stability against thermal stress at 85 °C over 250 h and retained ∼95% of its initial efficiency. This work demonstrates a significant step towards all-vacuum deposited perovskite solar cells with high thermal stability.

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The structural and optical properties of thermally evaporated PbSe/ZnSe multiple quantum well (MQW) structures as a function of the PbSe quantum well (QW) layer thickness in the range between 2.5 and 10 nm have been investigated. An ordered periodicity in the MQW structure was confirmed by transmission electron microscopy. The discrete linear resonances in the absorption spectra and the corresponding blue shift observed with decreasing well layer thickness unambiguously reflect the quantum confinement effect. The effective QW band gap is calculated from the infinite well approximation and compared to the experimentally observed value. The QW emission is identified and discussed.